This invention relates to solid state circuit interrupters employing digital electronic trip units. One such solid state circuit interrupter is described within U.S. Pat. No. 4,589,052, which Patent is incorporated herein for purposes of reference. Such electronic trip units are used in circuit interrupters and are capable of acting on a number of programmed parameters to interrupt the circuit being protected in a timely manner. One such electronic trip unit which allows for user interaction, provides capability both to select trip parameters and to view the selected trip parameters is found within U.S. Pat. No. 4,672,501, which Patent is also incorporated herein for purposes of reference.
For purposes of reducing cost while maintaining accuracy and functionality of the electronic trip units, microprocessors are being employed to gather information, process the information, and provide a means of monitoring the information using associated digital circuitry. The use of such microprocessors allows more protection functions to be contained in smaller-sized packages. Smaller-sized circuit interrupters, however, do not contain the means required to enter data or to view the data being processed. Typically with molded case circuit interrupters, the size of the case limits the amount of area available for such user-interface equipment. The user-interface equipment employed on larger-sized molded case circuit interrupters typically consists of rotatable switches or potentiometers on the cover with associated printed indicia to indicate the relative switch positions. The amount of area available on the cover of such circuit interrupters is also limited and hence reduces the number of optional features requiring additional switches and potentiometers.
A separate portable display and keypad in the form of a self-contained unit, powered by an internal power supply and which contains a microprocessor and associated circuitry and which communicates with the circuit interrupter trip unit by use of an infrared transmitter is described within U.S. Pat. No. 4,751,605. This arrangement requires a separate microprocessor and related digital circuitry within the portable display and keypad which adds to the overall costs of the circuit interrupter.
U.S. Pat. No. 4,814,712 "Test Kit for a Circuit Breaker Containing an Electronic Trip Unit" describes a separate portable display and keyboard unit that is capable of reading stored set points within an associated circuit interrupter but is incapable of changing the set point parameters. U.S. patent application Ser. No. 232,035 filed Aug. 15, 1988 entitled "Circuit Breaker with Removable Display and Keypad" also describes a keypad and display arrangement and is incorporated herein for reference purposes.
It would be advantageous to provide a user-interface unit to a circuit interrupter which interfaces with the electronic trip unit to display and set the electronic trip unit parameters while keeping the size and cost of the user-interface unit within practical economic limits. Additionally, the user-interface unit should contain display capability for all possible circuit interruption options by means of software located solely within the trip unit microprocessor.
Circuit interrupters that currently provide independent set point adjustment, position a removable cover over the adjustment means for security reasons. The cover is usually sealed to the housing of the circuit interrupter by means of a crimped security wire looped through a hole in the circuit interrupter housing and a hole in the cover. To change the settings of the trip unit, the wire must be cut, the cover removed and then replaced. This does not prevent unauthorized access, but merely provides an indication that such unauthorized access has taken place.
It would be advantageous to provide security to trip parameters stored within an electronic trip unit to prevent tampering or accidental modification of the trip unit settings without requiring a security wire.
Accordingly, one purpose of this invention is to provide a simple, inexpensive user-interface device which allows an operator to display and set the trip parameters of an electronic circuit interrupter while at the same time preventing unauthorized access to the trip parameters.
Another purpose of the invention is to provide a less expensive combined keypad display unit having all the features of state-of-the-art keypad and display units that are separately arranged on the circuit breaker cover.